JP2914219B2 - Analog video signal transmission device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a master device and a plurality of slave devices. The master device and each slave device transmit an analog video signal through a transmission path and transmit the analog video signal through the transmission path. The present invention relates to an analog video signal transmission device that corrects a video signal attenuation.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram showing an example of this type of analog video signal transmission device. As shown in the figure,
This device includes one parent device 1 and a plurality of child devices 20 and 2.
4 and 28, the parent device 1 and each of the child devices 20 and 2
4 and 28 are connected via repeaters 30 to 32, respectively. Here, the parent device 1 and each of the repeaters 30 to 32 are connected by a video signal transmission line 29 in which a plurality of analog video signal transmission lines and a plurality of control signal transmission lines are bundled. The child devices 20, 24, and 28 are connected to each other by video signal transmission lines 33 to 35 each including an analog video signal transmission line and a control signal transmission line.

A display control circuit 2 provided in the parent device 1 transmits image data held in the parent device 1 to a designated child device or receives a designated image data in response to an instruction from an operator of the parent device 1. It receives image data from the child device. The relays 30 to 32 relay the video signal. Each of the child devices 20, 24, and 28 has the same hardware configuration, is sequentially connected to the parent device 1, and has a display control circuit 19, 23, and 27 in each of the child devices 20, 24, and 28. In response to an instruction from the operator of the parent device 1, transmission of image data of the child device and reception of image data from the parent device 1 are performed.

Here, the image data transmitted through the video signal transmission path, that is, the analog video signal, has an attenuation amount corresponding to the distance of the transmission path between the parent device 1 and each child device. For this reason, conventionally, a correction circuit 1 is provided in each of the slave devices 20, 24, 28 so that such an amount of attenuation can be appropriately corrected.
8, 22, and 26 are provided. Then, this correction circuit 1
In 8, 22, and 26, the correction amount can be adjusted in three stages according to the length of each video signal transmission path from the parent device to each child device and from each child device to the parent device. That is, when the apparatus is installed, the length of the video signal transmission path is measured for each slave apparatus, and the amount of correction according to the transmission path length is adjusted by the switches 40 to 42 in each slave apparatus. Correction circuit 1
In steps 8, 22, and 26, the analog video signal is corrected based on the correction amounts adjusted by the switches 40 to 42.

[0005] Next, the operation of the analog video signal transmission device configured as described above will be described. When the operator of the parent device 1 requests, for example, reception of image data from the child device 24, the display control circuit 2 of the parent device 1 causes the child device 2
4 requests the transmission of analog video signals via the video signal transmission path 29 and the repeaters 30 and 31. Upon receiving this request, the display control circuit 23 in the slave device 24 transmits an analog video signal in its own device. In this case, the correction circuit 22 in the slave device 24 adds the correction amount selected by the switch 41 to the analog video signal transmitted from the display control circuit 23 and transmits the analog video signal as image data on the video signal transmission path 34. . When the display control circuit 2 in the parent device 1 receives the image data of the child device 24 via the repeaters 31, 30 and the video signal transmission line 29, it displays it on a display (not shown).

When the operator of the parent device 1 requests the connected child device to transmit the image data of the own device, the display control circuit 2 of the parent device 1 transmits the analog video signal to the child device. Declaration and at the same time the video signal transmission path 29
An analog video signal is sent out. Then, the transmitted analog video signal enters each slave device via the video signal transmission path 29 and each repeater. In each correction circuit of each slave device, when an analog video signal from the master device 1 is input, a correction amount selected by a corresponding switch is added to the input analog video signal and transmitted to each corresponding display control circuit. .
Each display control circuit displays the analog video signal as image data on a display (not shown).

As described above, an analog video signal transmitted between one master device 1 and a plurality of slave devices 20, 24, and 28 has an attenuation corresponding to the length of the video signal transmission path. From the respective correction circuits 1 in each of the slave devices 20, 24, 28
In steps 8, 22, and 26, the analog video signal is transmitted after being added with a correction amount set by the corresponding switch, and the received analog video signal is similarly corrected by the switch. The amount is added and displayed as image data.

Next, FIG. 5 shows an example of an automatic cable length measuring device in the case where the correction amount of such an analog video signal is obtained from the cable length which is the transmission line length. That is, when a signal is automatically transmitted from the transmitter 61 to the receiver 63 via the transmission cable 62 in which a plurality of signal transmission lines are bundled, the cable length automatic measuring device includes a high frequency of a specific frequency inside the receiver 63. The transmission cable 62 includes a high-frequency oscillator 64 for generating a signal, a cable length determination circuit 67 for determining a cable length, and transmission lines 65 and 66 for returning signals for measuring the distance of the cable in the transmission cable 62. ing.

Here, when measuring the cable length, first, the signal output from the high-frequency oscillator 64 is transmitted to the transmission line 65.
Once transmitted to the transmitter 61, then turned back by the transmitter 61, and then transmitted to the receiver 63 through the transmission line 66 and output to the cable length determination circuit 67. The cable length is automatically measured by the cable length determination circuit 67 detecting the signal delay amount of the high-frequency signal transmitted back.

[0010]

In the conventional analog video signal transmitting apparatus shown in FIG. 4, when the attenuation of the analog video signal transmitted on the transmission path is corrected, an installation worker is required to install the apparatus when installing the apparatus. Is measured, and each switch in the slave device is switched according to the measured amount to set a correction amount. For this reason, there is a drawback that an operation error is likely to occur and an appropriate correction is not performed when the operation error occurs. In addition, when replacing only a specific slave device or adding a slave device, it is necessary to measure the length of the transmission line again depending on the conditions of the installation location. The operation becomes very complicated, and as a result, there is a disadvantage that an operation error is caused.

On the other hand, in the cable length automatic measuring device shown in FIG. 5, although the length of the transmission line can be automatically measured,
When a plurality of child devices are connected to one parent device, the number of return transmission lines is required by the number of child devices. For this reason, the number of transmission lines increases, and the cross-sectional area of the cable becomes very large. As a result, there are disadvantages in that it is difficult to prepare the cable and the cable becomes expensive. Therefore, the present invention provides a method for correcting the attenuation of an analog video signal transmitted on a transmission line between one master device and a plurality of slave devices according to the length of the transmission line. An object of the present invention is to suppress the number of signal lines for transmitting a signal for measurement and to automatically measure the length of a transmission line.

[0012]

SUMMARY OF THE INVENTION In order to solve such a problem, the present invention provides a master device with a measurement start signal for starting a measurement of a distance of a video signal transmission line for correcting an analog video signal. Provide a generation circuit to generate, and input a measurement start signal to each child device, output a distance measurement signal, detect the output distance measurement signal, measure the distance of the video signal transmission path, and correct it to the correction circuit A first signal line for transmitting a measurement start signal between the parent device and each child device, and a second signal line for transmitting a distance measurement signal output from the child device to the parent device. And a third signal line for transmitting the distance measurement signal of the second signal line transmitted to the parent device from the parent device to the child device , and the measurement circuit inputs a measurement start signal immediately after power-on. Then, the distance measurement signal is transmitted to the second signal. And outputs to the line, when detecting the output distance measurement signal via a third signal line, in which so as to deliver a measurement start signal to the next stage of the child device. Further, a repeater is provided between the parent device and each child device, and the repeater relays an analog video signal, a measurement start signal, and a distance measurement signal.

[0013]

When the measurement start signal is output from the generation circuit of the parent device to the first signal line, the measurement circuit of the child device inputs the measurement start signal and outputs the distance measurement signal to the second signal line. When the distance measurement signal output from the second signal line is input to the slave device via the third signal line via the master device, the measurement circuit determines the input time of the distance measurement signal and the distance measurement signal. The distance of the video signal transmission path is measured from the time difference from the point at which is output to the second signal line. As a result, when correcting the amount of attenuation of an analog video signal transmitted on a video signal transmission path between one parent device and a plurality of child devices in accordance with the length of the transmission line, the transmission path length The number of signal lines for measurement may be only the first to third signal lines common to the devices, so that an increase in the number of signal lines can be suppressed and the transmission line length can be automatically measured. The measurement circuit outputs the distance measurement signal to the second signal line when the measurement start signal is input immediately after the power is turned on, and starts the measurement when the output distance measurement signal is detected via the third signal line. The signal is transmitted to the child device at the next stage. As a result, when measuring the distance of the video signal transmission path between the parent device and each child device, the measurement is automatically started immediately after the power is turned on, so that the analog video signal is corrected quickly and accurately. Can be. In addition, since the timing of distance measurement of the video signal transmission path performed by each measurement circuit of each child device can be completely arbitrated, it is possible to prevent the child devices from acquiring a distance measurement right.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an analog video signal transmission device according to the present invention. In this figure, the present apparatus is similar to the conventional apparatus shown in FIG.
A plurality of child devices 20, 24, and 28 are provided, and a relay device 3 is provided between the parent device 1 and each of the child devices 20, 24, and 28.
They are connected via 0-32. Here, a video signal transmission line 2 in which a plurality of analog video signal transmission lines and a plurality of control signal transmission lines are bundled between the parent device 1 and each of the repeaters 30 to 32.
9, each of the repeaters 30 to 32 and each of the slave devices 2
Between 0, 24, and 28, video signal transmission lines 33 to 35 each including an analog video signal transmission line and a control signal transmission line.
Are connected to each other. The parent device 1 is connected to each of the child devices 20, 24, and 28 via the video signal transmission path 29, each of the repeaters 30 to 32, and each of the video signal transmission paths 33 to 35.
And the transmission of analog video signals.

Here, the display control circuit 2 of the parent device 1 transmits the image data held in the parent device 1 to the designated child device in accordance with an instruction of the operator of the parent device 1 as in the conventional device, and The image data is received from the designated child device. Further, the master device 1 outputs a high-frequency signal used as a trigger for starting the distance measurement of the video signal transmission path by each slave device as a measurement start signal, and a measurement start signal generation circuit 3 that is transmitted from each slave device. A feedback unit 43 that returns the measurement signal via the upward return signal line 16 (second signal line) to the downward return signal line 44 (third signal line).
Is provided.

The repeaters 30 to 32 relay a video signal and various control signals in the same manner as the conventional apparatus, and also relay a measurement signal for measuring the distance of the video signal transmission path and a measurement start signal. That is, the measurement signal lines 6, 7, 10, 11, 14, 14, and 15 for transmitting the measurement signal of each slave device in each repeater are connected to the up and down return signal lines 16, 44.
Are connected to each other, the measurement signal is shared by all the connected child devices. Therefore, the measurement signal is transmitted to the parent device, the child device, and the lower child device in the repeater.
Divide into directions. In addition, the signal is output from the measurement start signal generation circuit 3 in the master device 1 and is output from the measurement start signal transmission lines 4, 5, 8,
The measurement start signal transmitted on 9, 12, 13 (first signal line) is used for arbitration of the distance measurement right of each child device.
In the repeater, the signal is divided into two signals, that is, a parent device (upper child device) and a lower child device.

Each of the child devices 20, 24, and 28 has the same hardware configuration, is sequentially connected to one parent device 1, and has a display control circuit in each of the child devices 20, 24, and 28. Reference numerals 19, 23 and 27 denote the parent device 1 as in the conventional device.
The image data of the child device is transmitted and the image data from the parent device 1 is received according to the instruction of the operator. In addition, after receiving the measurement start signal transmitted from the parent device 1, each child device immediately measures the distance of the video signal transmission path and determines a proper correction amount of the analog video signal. Circuits 17, 21, and 25 and a correction circuit similar to a conventional device for correcting an attenuation amount of an analog video signal caused by a distance of a video signal transmission path between a parent device and a child device when transmitting an analog video signal. 18, 22, and 26 are provided for each.

Next, FIG. 2 is a block diagram showing a main part of the analog video signal transmission device configured as described above, and shows, for example, an example of the distance measuring circuit 17 provided in the slave device 20. The distance measurement circuits of the other child devices have the same configuration. In the figure, the distance measuring circuit is a selector 5
0, flip-flops 51 to 53, 56, 58, gates 54, 57, oscillator 55, counter 59, and determination circuit 60. FIG. 3 is a timing chart showing operation waveforms of each unit of the distance measurement circuit 17 provided in the slave device 20. The operation of the main part of the present invention will be described with reference to the block diagram shown in FIG. 2 and the timing chart shown in FIG.

The reset (bar) signal shown in FIG. 2 is output once only from the reset circuit (not shown) in the child device 20 after the power is turned on as shown in FIG. At this time, the flip-flop 56,
Reset 58 to stabilize its state. by the way,
The measurement start signal generation circuit 3 in the above-described parent device 1 immediately starts outputting a 10 KHz clock pulse signal (that is, a measurement start signal) when the power is turned on to the parent device 1.
Thereafter, this clock pulse signal is continuously output until the power of the parent device 1 is turned off.

The measurement start signal thus generated is first sent to the child device 20 connected closest to the parent device 1 via the signal line 4.
And the selector 50 in the distance measuring circuit 17 decides whether to send it to the next child device (child device 24) or to measure the distance of the own device. The logic of the selector 50 is selected so as to input a measurement start signal via the signal line 4 to the flip-flop 51 of the own device after the power is turned on until the distance measurement of the video signal transmission path is performed once. That is, when the power of the parent device 1 is turned on and the measurement start signal is transmitted from the parent device 1, the distance measurement of the video signal transmission path is sequentially performed from the child devices close to the parent device 1. As a result,
The timing of distance measurement does not overlap between the child devices, so that all child devices can perform distance measurement using the same measurement start signal and measurement signal.

Here, the actual distance measurement is performed as follows. That is, the measurement start signal via the signal line 4 is shown in FIG.
Are input as shown in FIG.
3 transmits the measurement start signal to the oscillator 5 shown in FIG.
100 MHz 10 times faster than the above measurement start signal from 5
3D. As a result, a measurement signal as shown in FIG.
Output to signal line 7. The measurement signal output to signal line 7 enters return signal line 16 and returns to feedback unit 4 in parent device 1.
It is folded at 3. Then, the folded measurement signal passes through the folded signal line 44, and further passes through the signal line 6 as shown in FIG.
The process returns to the distance measurement circuit 17 in the child device 20 as a signal as shown in FIG.

Here, the time until the measurement signal output from the signal line 7 returns to the signal line 6 is held by the flip-flop 56. Therefore, the delay time of the measurement signal is measured by counting the clock signal shown in FIG. 3E from the oscillator 55 input through the gate 57 by the counter 59 during this time. This delay time is used as it is as a result of the distance measurement of the video signal transmission path.
That is, the determination circuit 60 determines the output of the counter 59 to determine an appropriate analog video signal correction amount, and notifies the correction circuit 18. The correction circuit 18 corrects the analog video signal based on the correction amount determined from the distance measurement result of the video signal transmission path.

When the measurement signal output from the signal line 7 returns to the signal line 6, the output of the flip-flop 58 rises as shown in FIG. Accordingly, the selector 50 operates according to the output signal, and the selector 50 shown in FIG.
The signal line 4 and the signal line 5 are connected as shown in FIG. As a result, the measurement start signal is transmitted to the next distance measurement circuit 21 in the child device 24, so that the distance measurement circuit 21 of the child device 24 operates similarly to the distance measurement circuit 17 of the child device 20, Execute the distance measurement of the video signal transmission path. Then, when the distance measurement of the video signal transmission path in the child device 24 is completed, the distance measurement of the video signal transmission line is performed in the child device 28 next.

As described above, when measuring the distance of the video signal transmission path between the parent device and each child device, the measurement is automatically started immediately after the power is turned on. Can be done accurately. Further, even when a plurality of child devices are connected to one parent device, the distance measurement signal line is not provided for each child device, but is shared by each child device. The distance of the video signal transmission path can be automatically measured with only three lines. Further, since the timing of the distance measurement of the video signal transmission path performed by each distance measurement circuit of each slave device is completely arbitrated, the slave devices do not have any right to measure the distance.

When the measurement of the distance of the video signal transmission path in each slave device is completed, transmission of image data between the master device 1 and each slave device in accordance with the instruction of the operator of the master device 1 is performed. . That is, when the operator of the master device 1 requests reception of image data from the slave device 24, the display control circuit 2 of the master device 1 sends the slave device 24 to the slave device 24 via the video signal transmission path 29 and the repeaters 30, 31. Request transmission of analog video signals. Display control circuit 23 in slave device 24
Receives this request and transmits the analog video signal in its own device. In this case, the correction circuit 22 in the child device 24
Adds the correction amount determined by the distance measurement circuit 21 to the analog video signal sent from the display control circuit 23, and transmits the same as image data on the video signal transmission path 34. When the display control circuit 2 in the parent device 1 receives the image data of the child device 24, it displays it on a display (not shown).

When the operator of the parent device 1 requests the connected child device to transmit the image data of the own device, the display control circuit 2 of the parent device 1 transmits the analog video signal to the child device. Declaration and at the same time the video signal transmission path 29
An analog video signal is sent out. Then, the transmitted analog video signal enters each slave device via the video signal transmission path 29 and each repeater. When the analog video signal from the parent device 1 is input to each correction circuit of each slave device, the correction amount determined by the respective distance measurement circuit is added to the input analog video signal and transmitted to the corresponding display control circuit. I do. Each display control circuit displays the analog video signal as image data on a display (not shown).

[0027]

As described above, according to the present invention, when the measurement start signal is output from the generation circuit of the parent device to the first signal line, the measurement start signal is input to the measurement circuit of the child device. When the distance measurement signal is output to the second signal line and the distance measurement signal output from the second signal line is input to the child device via the parent device and the third signal line, the measurement circuit Is
The input time of the distance measurement signal and the distance measurement signal
Since the distance of the video signal transmission path is measured from the time difference from the point of time when the video signal is output to the signal line, the analog signal transmitted on the video signal transmission path between one master device and a plurality of slave devices is measured. When correcting the amount of attenuation of the video signal according to the length of the transmission line, it is only necessary to increase the first to third signal lines common to each device. An increase in the number of signal lines to be transmitted can be suppressed, and the length of the transmission line can be automatically measured. The measurement circuit is
When a measurement start signal is input immediately after the power is turned on, the distance measurement signal is output to the second signal line, and when the output distance measurement signal is detected via the third signal line, the measurement start signal is output to the next child. Since it is sent to the device, when measuring the distance of the video signal transmission path between the parent device and each child device, since the measurement can be started automatically immediately after turning on the power,
Correction of an analog video signal can be performed quickly and accurately. In addition, since the timing of distance measurement of the video signal transmission path performed by each measurement circuit of each child device can be completely arbitrated, it is possible to prevent the child devices from acquiring a distance measurement right.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram of a distance measuring circuit showing a main part of the apparatus of the embodiment.

FIG. 3 is a timing chart showing the operation timing of each unit of the distance measurement circuit.

FIG. 4 is a block diagram showing a configuration of a conventional device.

FIG. 5 is a block diagram showing a configuration of another conventional device.

[Explanation of symbols]

1: Parent device, 2, 19, 23, 27 ... Display control circuit, 3
... Measurement start signal generation circuit, 4, 5, 8, 9, 12, 13
... Measurement start signal transmission path, 6, 7, 10, 11, 14, 1
5 ... measurement signal line, 16, 44 ... return signal line, 1
7, 21, 25: distance measurement circuit, 18, 22, 26: correction circuit, 20, 24, 28: slave device, 29, 33 to 35
... Video signal transmission path, 43 ... Feedback part, 50 ... Selector, 5
1 to 53, 56, 58 ... flip-flops, 54, 57
... gate, 55 ... oscillator, 59 ... counter, 60 ... determination circuit.

Claims (2)

(57) [Claims] An information processing apparatus comprising: a master device; and a plurality of slave devices connected to the master device via a video signal transmission path. The master device and each slave device include a display control circuit, and each slave device includes a correction circuit. The parent device and each slave device perform transmission of an analog video signal via the display control circuit and the video signal transmission line, and each of the slave devices is configured to attenuate the analog video signal passing through the video signal transmission line. An analog video signal transmission device that corrects an amount by the correction circuit, wherein the generation device generates a measurement start signal for starting measurement of a distance of the video signal transmission path for correcting the analog video signal to the master device. Provided, and in each of the child devices,
A master circuit for inputting the measurement start signal, outputting a distance measurement signal, detecting the output distance measurement signal, measuring the distance of the video signal transmission path, and providing the distance as a correction amount to the correction circuit; A first signal line for transmitting the measurement start signal, a second signal line for transmitting the distance measurement signal output from the child device to a parent device, and a signal line transmitted to the parent device between the child devices. The distance measurement signal of the second signal line is connected to a third signal line for transmitting the distance measurement signal from the master device to the slave device , and the measurement circuit inputs the measurement start signal immediately after power-on.
When the force is applied, the distance measurement signal is output to the second signal line.
And outputs the output distance measurement signal to a third signal line.
When the measurement start signal is detected through the
It is sent to an analog video signal transmission apparatus according to claim. 2. The analog video signal transmission device according to claim 1 , further comprising a repeater between the master device and each of the slave devices, wherein the repeater is an analog device.
Video signal, the measurement start signal and the distance this relays measurement signal <br/> analog video signal transmission apparatus according to claim.